(i) Field of the Invention
The present invention relates to the production of pellets from highly absorptive solid materials "fines" i.e. particles of a size of less than 30-50 mesh, expecially useful as cat litter.
(ii) Description of the Prior Art
For the purpose of this invention, the term "highly absorptive solid material" is defined as clays, diatomaceous earths, Fuller's earths, and bentonites, that are low in bulk density, usually less than about 45 lbs/cu. ft., and have the ability to absorb liquids into their pores. Such materials usually contain more than one component but most often have a high percentage of kaolinite, or attapulgite, or montmorillonite, or sepiolite, or diatomite. Generally such a material that has any of the above as the major component is very likely to have lesser amounts of one or all of the others. Any of the other known clay minerals, e.g. kaolinite and illite are commonly present and non-clay minerals and/or siliceous materials that cannot be classified as diatomaceous earth may be present. Typical of the latter is silica sand, limestone, iron oxide and gypsum.
Another useful clay material is Georgia clay. Georgia clay is a naturally occurring clay mineral consisting predominantly of the clay mineral kaolinite, a crystalline hydrated aluminum silicate of the formula Al.sub.2 O.sub.3.2SiO.sub.2.2H.sub.2 O. This clay mineral is rarely found pure, but is the main constituent of kaolin whose composition is about 40% alumina, about 55% silica, plus impurities and water. Kaolin is also known as china clay; white bole; argilla; porcelain clay; white clay; and is a white-burning clay, which, due to its great purity, has a high fusion point and is the most refractory of all clays.
Such materials, which are used as industrial absorbents, soil conditioners, decorative mulch herbicides, insecticide carriers, cat box absorbent and sanitary absorbents, are generally mined, dried and/or calcined, crushed and screened to a particle size, which depends on the particular use to which it will be applied. This crushing and screening inevitably leads to a waste product known as "fines", which can be defined as a range of particles less than 30-50 mesh in size. While the "fines" from some specially selected and/or further processed such material can be used, for instance, attapulgite as drilling mud, it is generally accepted within the industry that such materials which are best suited as an absorbent or for decorative purposes and which grade down from 30-50 mesh have little market demand. In some products, depending on desired final particle size "fines" can be generated in an amount equal to about 10% to about 60% of the final merchantable product and for some products, e.g. 16/30, 30/60 and 24/84 insecticide grades, the "fines" lost will be on the high side of the above range. Obviously, if these "fines" cannot be used they represent an economic loss to the manufacturer and in fact created a disposal problem.
Various methods have been advanced for pelletizing "fines" which generally involve processing the "fines" by compressing them into pellets of a useable size. These methods have proven satisfactory for pelletizing plastic, nonabsorbent clay "fines". Processes for pelletizing sorptive mineral "fines" which use colloidal clay as a binder by agglomeration have also been advanced but for the most part have been unsatisfactory because it is difficult to control the pellet size and strength and the resulting pellets are unstable under certain environmental conditions and lack the qualities of the sorptive mineral.
Procedures have been proposed for treating such clays to enable the production of pastes and/or pellets therefrom. In one procedure, in U.S. Pat. No. 1,394,241 patented Oct. 18, 1921, by E. Weber, clay pastes are provided which contain, in addition to water, various vegetable extracts. Such vegetable extracts include the saponaceous bodies and extracts or matter having their origin from the disintegration of cellulose (lignin). Among the useful saponaceous substances were pure saponins, githagin, quillaja and senegin. Extracts of any saponin-bearing plants, barks, roots, bulbs, fruits, such as of the quillaia, of soapwort, a cock-wheed, of sow-breads, and more generally of the saponin-bearing plants, as well as decoctions of ivy and of capsules of the chestnut, and neutral water soluble saponins were also said to be useful. In addition cellulose-waste and cellular pitch, alkaline waste-lyes and sulfite-cellulose may also be used.
The object of such addition was, however, not to be able to produce absorptive pellets from clay fines, but, in fact to improve the pouring of clay-pastes or unplastic stiff pulps through the use of alkali, mixed with a small percentage of those vegetable extracts.
Allen, in U.S. Pat. No. 2,765,238 patented Oct. 2, 1956, provided reinforcing pigment produced by precipitating lignin from an aqueous solution in which there is hydrated silica or silicate, or a mixture thereof. The hydrated silica and silicate could be present either in the aqueous solution or suspended therein in very finely divided form. In the product, lignin was preferably present as a coating. The aim of that invention was, however, to provide calcium silicate pigment which could be used in rubber compounding and which would disperse well in rubber. There is no subbestion of providing absorptive pellets from clay fines.
Gmeiner, in U.S. Pat. No. 2,839,415 patented June 17, 1958, provided a procedure for the manufacture of clay products, which involved the addition of waste sulfite liquor, which had been previously concentrated to the natural clay and/or shale body. This is the liquor which results from the treatment of wood in making pulp by the sulfite process, wherein the cellulose fibers are liberated from the wood by the employment of an aqueous solution of sulfurous acid in which a calcium, magnesium or ammonia base has been dissolved. The waste sulfite liquor thus obtained contains the soluble products of digestion, which amount to about 50 percent or more of the original wood substance. Although the exact composition of the waste liquor is not completely known it is believed to include lignin, carbohydrates, proteins, resin, fat, sulfur dioxide combined with lignin, and the calcium salt of lignosulfonic acid for the magnesium or ammonia salt, if either of the latter are used as a base for the sulfurous acid used in the digestor. It also contains lignin sulfonates, i.e. metallic sulfonate salts made from the liquor of sulfur pulp mill liquors. The patentee was concerned with the problem of improving the strength, both in the unfired and fired state of clay products, and, therefore, reduce the loss in manufacturing and handling. That patentee was not concerned with the provision of absorptive pellets from clay fines.
Herdrich in U.S. Pat. No. 3,536,503 patented Oct. 27, 1970, provided a bloated clay by adding a solution of additives to the clay which, during the dripping process were capable of forming a solidified shell around the granule. The additives acted as binders and were set or cured at low temperatures below about 300.degree. C., preferably just above about 100.degree. C. One suitable solution suggested was, sulfite waste liquor which had the advantage of being economic and available in large amounts. Powdered fluxing agents and gastifiable bloating adjuvants were also added in suspension or emulsion. This patentee thus intended to provide a combination of additives which allowed converting almost any plastic clay to a bloating clay of desired low bulk density and low water absorbency. He was not concerned with the provision of absorptive pellets from clay fines.
Parmella, in Canadian Pat. No. 641,299 issued May 15, 1902, provided a process for the production of pellets from particulate solid materials which comprised forcing the particulate material through a cylindrical die of such proportions that the ratio of the diameter to the length in the range of 1:5 to 1:15, the die having been previously conditioned by forcing therethrough particulate material comprising a lubricant. The patentee was thus concerned with a pelletizing of powdered material to produce pellets which had good mechanical strength. He was not concerned with the provision of absorptive pellets from clay fines.
Valenta, in U.S. Pat. No. 4,036,928 patented July 19, 1977, addressed the problem of pelletizing absorptive clay fines for use as, e.g. animal liter. According to that patentee, "fines" of a sorptive mineral, e.g., fuller's earth or diatomaceous earth, were mixed with sufficient moisture to just fill the pore space in the particles. In one instance water was added in an amount equal to between about 30 to about 45 percent by weight to the "fines". Once the "fines" and moisture were mixed in a cement-type mixer, ribbon blender or other suitable mixing device, they were then placed in a pelletizing machine were the moistened "fines" were compactly formed into pellets by forcing the mixture through a die. After the pellets were formed they were cut to the desired size. The pellets were then dried, driving the water from the pore space, with the result that the pellets had substantially the same absorbent capacity and bulk density as the original material.
The process was not, however, economically viable because of the added expensive drying step after the pellets had been formed.
Animal litter had also been made from waste rejects from a secondary fiber plant. In U.S. Pat. No. 4,341,180 patented July 27, 1982, by L. R. Cortigene et al, an animal litter was provided by the steps of partially de-watering waste rejects from a secondary fiber plant to a consistency such that the partially de-watered waste could be formed into pellets, forming the partially de-watered waste into pellets, and then drying the pellets, in which the partially de-watered waste contained from about 32 percent to about 40 percent water. The animal litter so prepared comprised pelleted and dried rejects of a secondary fiber plant containing a deodorizer material produced by de-watering rejects of a secondary fiber plant, cutting the rejects into small pieces, incorporating therewith a deodorant material, pelletizing and drying.
The deodorant material, advantageously, is sodium bicarbonate which, advantageously, is present in an amount of between about 1 percent to about 10 percent, preferably about 5 percent, based on the dry weight of the litter. The sodium bicarbonate may be partially or totally replaced by other suitable deodorants, for example, chlorophyll, sodium dihydrogen phosphate, potassium dihydrogen phosphate, potassium acid phthalate, the water soluble constituents of cherry pits, 2-isopropoxycamphane, 2(.alpha.-hydroxyethoxy)camphane, and the like. Additionally, there may be included bactericides such as cetylperidium chloride, cetalkonium chloride, and the like, which function both as bactericide and as a surfactant. There may also be included antioxidants, mold inhibitors such as propionic acid and its salts, and phenols and phenolic salts such as sodium pentachlorophenol. Pigments and dyes may also be included, most advantageously, in the slurry fed to the vacuum filter, for example, along with the flocculating agent added to improve the filtration.
The basic animal litter composition of that invention is prepared from rejects of a secondary fibre plant. The solids in these rejects consist essentially of about 50 percent to about 90 percent cellulose and from about 10 percent to about 50 percent paper-making mineral filler which is chiefly kaolin or china clay. These rejects are de-watered, cut into pieces, mixed with the deodorant or other additives, pelletized and dried. To give a pelleted and dried material containing in addition to the solids of the rejects which consist of about 50 percent to about 90 percent cellulose and about 10 percent to about 50 percent mineral filler, about 1 percent to about 10 percent deordorizing material on a dry weight basis.
This patent, as well, was not commercially attractive because of the amount of calorific energy needed to dry the pellets, which initially contained from 32-40% water.
It is therefore one object of this invention to provide a commercially useful process for pelletizing clay "fines" to form absorptive pellets of useful size.
It is another object of this invention to provide a commercially useful process for pelletizing clay "fines" into absorptive pellets of useful strength.